Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural
sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS
Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing
UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.

The aim of this work was to examine the influence of changes in plasma renin activity and aldosterone concentration on osmotic pressure of blood plasma in calves in the neonatal period. The examination was carried out on 11 calves of black  white breed directly after birth and in the 2nd, 3rd, 7th and 30th day of life. Plasma renin activity and aldosterone concentration were examined by means of radioimmunological methods, while the osmotic pressure  by means of the cryoscopic method. The decrease of plasma renin activity to the value of 1,55 ng/ml/h was proved in the first week of life, and it remained at this level till the end of the first month of calves life. The aldosterone concentration was high after birth (61pmol/l) and decreased rapidly during the first 24 hours. Gradual increase of concentration of this hormone (to 85 pmol/l) was observed from the 2nd to the 7th day, and its decrease  till the end of the first month of life. The